The use of metal cans in the beverage and food processing industries has increased dramatically over the past several decades and continues to increase. In an effort to reduce costs and preserve resources, it is desirable to manufacture metal cans with extremely thin side walls. Thus, the machines that form, trim and otherwise handle metal cans must be able to process cans in large volumes and at high speeds without damaging the relatively thin side walls.
It is conventional practice to form an unfinished can having a cylindrical configuration with a closed bottom portion and a cylindrical side wall that is open at the top end. Unfinished cans may be formed by a variety of processes including impact extrusion and deep drawing processes whereby a generally circular flat metal plate or sheet is first passed through an impact extrusion or deep drawing press where it is formed into a relatively shallow cup. The cup is then passed through an ironing press which elongates the side walls and produces a can having the desired wall thickness.
It is not possible, however, to produce a can by an extrusion or drawing process having the exact height required or having a side wall with a uniform upper edge. can bodies as initially formed are usually of non-uniform height and have irregular edges at the open top end. Subsequent to the formation of the unfinished container, it is necessary to trim the upper end of the cylinder to produce a can of a fixed height having a smooth upper edge.
It is essential that the upper edge of a can be smooth and uniform. The operation employed in many devices of the prior art for trimming or forming the upper edge of the can to attach a can lid often produces an uneven or cracked perimeter which, of course, can result in an inadequate seal between the lid and the upper edge of the can. Any imperfections such as burrs or cracks will prevent a proper seal between the lid and the can in the upper edge area.
Moreover, any metal slivers or shavings produced by an uneven circumferential cut about the can will render the can unsuitable for use in the beverage and food processing industries. Thus, the formation of a smooth upper edge is essential to efficient can making.
As an additional matter, the scrap material trimmed from the can should be efficiently separated from the trimmed can during the cutting process to avoid jamming the machine.
The elimination of such imperfections is a particularly troublesome matter in the can making industry. An apparatus is needed to avoid these problems by efficiently trimming the can with a uniform and even circumferential cut and discarding the scrap separate from the trimmed can. The irregular open edge of the can must be evenly trimmed without imperfections to produce identical mass-produced cans which can be efficiently sealed.